A light sensor is suitably used for control of switching on and off of a lamp mounted on a vehicle.
The light sensor includes a light receiving element and a light guiding element for introducing the light to the light receiving element. The light is entered from the outside of the vehicle into the compartment of the vehicle via a windshield, and the light is introduced to the light receiving element through the light guiding element. This light sensor is disclosed in JP-A-2002-500769 corresponding to U.S. Pat. No. 6,376,824.
The light sensor is attached to a surface of the windshield on a compartment side (i.e., an inside of the vehicle) so that the brightness of the outside of the vehicle is accurately detected. Accordingly, the light guiding element is arranged near the surface of the windshield on the compartment side.
In an automatic lighting system of the vehicle, the lamp is controlled to turn on and off on the basis of the brightness of the outside in front of the vehicle, which is detected by the light sensor. For example, even if it is not necessary to turn on the lamp such as a head lamp since the outside of the vehicle is bright during the daytime, when the vehicle approaches a tunnel in front of the vehicle, it is preferable to turn on the head lamp. In this case, it is necessary to detect the tunnel before the vehicle reaches the entrance of the tunnel. Further, when the vehicle approaches an overpass in front of the vehicle during the daytime, it is preferable to pass under the overpass without turning on the head lamp. To control the head lamp in this manner, it is preferable to introduce the light only from the forward of the vehicle into the light sensor.
In a conventional tight sensor, the light guiding element for introducing the light to the light receiving element through the windshield is arranged behind the windshield. In general, the windshield is inclined toward the front of the vehicle. Specifically, the top of the windshield is disposed on the rear side of the vehicle, and the bottom of the windshield is disposed on the front side of the vehicle. Accordingly, an entrance surface of the light guiding element in the conventional light sensor is also inclined toward the front of the vehicle so that the entrance surface is in parallel to the windshield. The entrance surface of the light guiding element faces the windshield. Thus, not only the light from the forward of the vehicle but also the light from the upside of the vehicle are introduced into the entrance surface of the light guiding element. Specifically, the light along with the horizontal direction and the light in the vertical direction are entered into the entrance surface. Accordingly, it is difficult to detect the brightness in front of the vehicle with high accuracy.
Another conventional illuminant sensor includes a light guiding element having an entrance surface, which provides a convexity lens. Thus, the entrance surface is formed to have a spherical surface, the convexity of which faces the windshield. In this case, the light from the forward of the vehicle, the light from the upside and downside of the vehicle and the light from the right side and the left side of the vehicle are entered into the entrance surface of the light guiding element. Thus, it is difficult to detect the brightness in front of the vehicle with high accuracy.
In view of the above difficulty, it is required to detect the brightness in front of the vehicle with high accuracy.